Gas turbine engine with twin offset gas generators

ABSTRACT

A gas turbine engine comprises a fan on an engine central axis. Plural gas generators are downstream of the fan, each along a respective central axis, mutually offset, and offset from the engine central axis. A fan drive turbine is on the engine central axis, downstream of the dual gas generators, and driven by output from the dual gas generators, to drive the fan.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Patent ApplicationNo. 61/933,353, filed Jan. 30, 2014.

BACKGROUND OF THE INVENTION

This application relates to a gas turbine engine having a plurality ofoffset engine cores.

Gas turbine engines are known and, typically, include a fan deliveringair into a bypass duct as propulsion air. The air is also delivered intoa core engine where it passes to a compressor. Compressed air is passedinto a combustor where it is mixed with fuel and ignited. Products ofthis combustion pass downstream across turbine rotors driving them torotate.

Historically, the fan, compressor rotors and turbine rotors all rotatedabout a common axis.

Recently, it has been proposed to offset the core engine such that itextends along an axis which is non-parallel to the axis about which thefan rotates. This has advantages in that it may allow the overall lengthof the engine to be reduced.

SUMMARY OF THE INVENTION

In a featured embodiment, a gas turbine engine comprises a fan on anengine central axis. Plural gas generators are downstream of the fan,each along a respective central axis, mutually offset, and offset fromthe engine central axis. A fan drive turbine is on the engine centralaxis, downstream of the dual gas generators, and driven by output fromthe dual gas generators, to drive the fan.

In another embodiment according to the previous embodiment, the gasgenerators each include at least one compressor, a turbine and anintermediate combustor.

In another embodiment according to any of the previous embodiments, thefan drive turbine is driven by products of combustion which have passeddownstream over the gas generator turbines.

In another embodiment according to any of the previous embodiments, thegas generators each include a generator exhaust duct extending towardthe engine central axis from the gas generator turbine to deliver theproducts of combustion into an exhaust housing and across the fan driveturbine.

In another embodiment according to any of the previous embodiments, thegenerator exhaust ducts extend at an angle which extends toward theengine central axis at a more dramatic angle than a direction of therespective central axes of gas generators.

In another embodiment according to any of the previous embodiments, anacelle surrounds the fan rotor and receives bypass air for propulsion.

In another embodiment according to any of the previous embodiments,inlets into the generators are spaced circumferentially in the path ofair delivered by the fan into the nacelle.

In another embodiment according to any of the previous embodiments, abypass ratio is defined as a volume of air not passing into the inlets,compared to a volume of air passing into the inlets, with the bypassratio being greater than or equal to about 5.0.

In another embodiment according to any of the previous embodiments,struts connect the nacelle to the exhaust housing.

In another embodiment according to any of the previous embodiments, theplurality of gas generators is two.

In another embodiment according to any of the previous embodiments,struts connect the nacelle to the exhaust housing.

In another embodiment according to any of the previous embodiments, thegas generators each include a generator exhaust duct extending towardthe engine central axis from the gas generator turbine to deliver theproducts of combustion into an exhaust housing and across the fan driveturbine.

In another embodiment according to any of the previous embodiments, thegenerator exhaust ducts extend at an angle which extends toward theengine central axis at a more dramatic angle than a direction of therespective central axes of gas generators.

In another embodiment according to any of the previous embodiments, anacelle surrounds the fan rotor and receives bypass air for propulsion.

In another embodiment according to any of the previous embodiments,inlets into the gas generators are spaced circumferentially in the pathof air delivered by the fan into the nacelle.

In another embodiment according to any of the previous embodiments, abypass ratio is defined as a volume of air not passing into the inlets,compared to a volume of air passing into the inlets, with the bypassratio being greater than or equal to about 5.0.

In another embodiment according to any of the previous embodiments, anacelle surrounds the fan rotor and receives bypass air for propulsion.

In another embodiment according to any of the previous embodiments,inlets into the core engines are spaced circumferentially in the path ofair delivered by the fan into the nacelle.

In another embodiment according to any of the previous embodiments, abypass ratio is defined as a volume of air not passing into the inlet,compared to a volume of air passing into the inlets, with the bypassratio being greater than or equal to about 5.0.

In another embodiment according to any of the previous embodiments, agear reduction is positioned between the fan drive turbine and the fan.

These and other features may be best understood from the followingdrawings and specification.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a gas turbine engine.

FIG. 2 shows a detail of a portion of the gas turbine engine.

FIG. 3 is a perspective view of the gas turbine engine.

FIG. 4 shows a detail.

DETAILED DESCRIPTION

FIG. 1 shows a gas turbine engine 20 having a nacelle 22 receiving a fanrotor 24 driven by a fan drive shaft 26. A pair of core engines, or gasgenerators 28 and 30, are positioned to receive air from the fan 24. Thefan delivers air into the nacelle 22 as bypass air, but a portion of theair from circumferentially separate locations passes into the gasgenerators 30 and 28. Each gas generator includes a compressor section32 driven by a shaft 34 which is, in turn, driven by a turbine 36. Acombustor section 29 is positioned intermediate the compressor 32 andturbine 36. Exhaust ducts 38 and 40 extend downstream of the location ofthe turbine 36 into an exhaust housing 42. The products of combustion,downstream of the turbine rotor 36, pass across a fan drive turbine 42which is driven to rotate to, in turn, rotate the fan drive shaft 26and, thus, the fan rotor 24. A downstream end 47 of the engine is at theend of an exhaust housing 46. The gas generators 30 and 28 are mutuallyoffset, or angularly skewed. Their exhaust powers the downstream fandrive turbine 42 that, in turn, drives an upstream fan drive shaft 26. Agear reduction 300 might be included between fan drive turbine 42 andfan rotor 24 to lower the speed of rotation of fan rotor 24 relative tothe speed of fan drive turbine 42.

As can be appreciated from FIG. 1, the shaft 26 and, hence, the turbine42 and fan rotor 24 rotate along an axis X. The core engines 28 and 30extend along a direction Z (although in opposed directions) which isnon-parallel to the axis X. In fact, the direction Z extends inwardlytoward the axis X at a first angle. As can be appreciated, the exhaustducts 38 and 40 extend along a direction Y which is at a more dramaticangle inwardly toward the axis X.

FIG. 2 shows details of the engine 20 including the directions X, Y andZ. As can be appreciated, the free turbine 42 receives air from bothducts 38 and 40. The use of the double cores allows a reduction in theoverall length of the engine.

Returning to FIG. 1, struts 100 and 102 connect the fan drive turbinehousing 44 to the nacelle 22.

FIG. 3 shows a detail of the engine 20 including the fan rotor 24 at aforward end, the exhaust housing 44 and free turbine housing 44, and theducts 38 and 40.

As can be seen in FIG. 2, there are inlets 33 and 31 into the coreengines 30 and 28, such that the inlets are at circumferentially spacedlocation in a path of the bypass air within the nacelle 22.

The gas turbine engine 20 has a fan 24 on an engine central axis X.Plural gas generators 28 and 30 are downstream of the fan 24, each alonga respective central axis Z that are mutually offset and offset from theengine central axis X. A fan drive turbine 42 is on the engine centralaxis X, downstream of the dual gas generators 28, 30, and driven byoutput from the dual gas generators, for driving the fan 24.

The gas generators 28 and 30 include a generator exhaust duct 38, 40extending toward the engine central axis X from the gas generatorturbines 36 to deliver the products of combustion into an exhausthousing 44 and across the fan drive turbine 42. The exhaust ducts 38, 40extend at an angle Z which extends toward the engine central axis X at amore dramatic angle Y than a direction of the respective central axes Zof the gas generators 28, 30.

The circumferential spacing of inlets 31 and 33 is clear in FIG. 4. Theremaining flow path (outside of inlets 32 and 33) provides propulsion. Abypass ratio of the volume of air not passing into inlet 31 or 33compared to the volume that does pass into an inlet 31 or 33 is greaterthan or equal to 5.0 and less than or equal to 30.0.

Although an embodiment of this invention has been disclosed, a worker ofordinary skill in this art would recognize that certain modificationswould come within the scope of this invention. For that reason, thefollowing claims should be studied to determine the true scope andcontent of this invention.

1. A gas turbine engine comprising: a fan on an engine central axis;plural gas generators downstream of the fan, each along a respectivecentral axis that are mutually offset and offset from the engine centralaxis; and a fan drive turbine on the engine central axis, downstream ofthe dual gas generators, and driven by output from the dual gasgenerators, for driving the fan.
 2. The gas turbine engine as set forthin claim 1, wherein said gas generators each include at least onecompressor, a turbine and an intermediate combustor.
 3. The gas turbineengine as set forth in claim 2, wherein said fan drive turbine is drivenby products of combustion which have passed downstream over said gasgenerator turbines.
 4. The gas turbine engine as set forth in claim 3,wherein said gas generators each include a generator exhaust ductextending toward said engine central axis from said gas generatorturbine to deliver the products of combustion into an exhaust housingand across said fan drive turbine.
 5. The gas turbine engine as setforth in claim 4, wherein said generator exhaust ducts extend at anangle which extends toward said engine central axis at a more dramaticangle than a direction of said respective central axes of gasgenerators.
 6. The gas turbine engine as set forth in claim 5, wherein anacelle surrounds said fan rotor and receives bypass air for propulsion.7. The gas turbine engine as set forth in claim 6, wherein inlets intosaid generators are spaced circumferentially in the path of airdelivered by said fan into said nacelle.
 8. The gas turbine engine asset forth in claim 7, wherein a bypass ratio is defined as a volume ofair not passing into said inlets, compared to a volume of air passinginto said inlets, with said bypass ratio being greater than or equal toabout 5.0.
 9. The gas turbine engine as set forth in claim 7, whereinstruts connect said nacelle to said exhaust housing.
 10. The gas turbineengine as set forth in claim 7, wherein said plurality of gas generatorsis two.
 11. The gas turbine engine as set forth in claim 6, whereinstruts connect said nacelle to said exhaust housing.
 12. The gas turbineengine as set forth in claim 1, wherein said gas generators each includea generator exhaust duct extending toward said engine central axis fromsaid gas generator turbine to deliver the products of combustion into anexhaust housing and across said fan drive turbine.
 13. The gas turbineengine as set forth in claim 12, wherein said generator exhaust ductsextend at an angle which extends toward said engine central axis at amore dramatic angle than a direction of said respective central axes ofgas generators.
 14. The gas turbine engine as set forth in claim 13,wherein a nacelle surrounds said fan rotor and receives bypass air forpropulsion.
 15. The gas turbine engine as set forth in claim 14, whereininlets into said gas generators are spaced circumferentially in the pathof air delivered by said fan into said nacelle.
 16. The gas turbineengine as set forth in claim 15, wherein a bypass ratio is defined as avolume of air not passing into said inlets, compared to a volume of airpassing into said inlets, with said bypass ratio being greater than orequal to about 5.0.
 17. The gas turbine engine as set forth in claim 1,wherein a nacelle surrounds said fan rotor and receives bypass air forpropulsion.
 18. The gas turbine engine as set forth in claim 17, whereininlets into said core engines are spaced circumferentially in the pathof air delivered by said fan into said nacelle.
 19. The gas turbineengine as set forth in claim 18, wherein a bypass ratio is defined as avolume of air not passing into said inlet, compared to a volume of airpassing into said inlets, with said bypass ratio being greater than orequal to about 5.0.
 20. The gas turbine engine as set forth in claim 1,wherein a gear reduction is positioned between the fan drive turbine andthe fan.